The present invention relates to a mechanism for charging the mirror and shutter in a video still camera which uses a magnetic recording disk instead of a film as recording medium.
The recent trend in a photographic camera is toward an automatic film winding camera having a motor contained therein for automatically cocking, or charging, a shutter and a mirror and winding a film as soon as the shutter is released to complete an exposure. Recently a video still camera, which uses a magnetic recording disk instead of a film as a recording medium, has been developed. Video still cameras are free from the need for film winding unlike a photographic camera, but require the shutter and mirror to be charged like a photographic camera. In the video still camera there are three methods of charging the shutter and the mirror. One method is to charge the mirror and the shutter at the same time. According to another method, the shutter is charged after the mirror has been charged. In still another method the shutter charge is initiated while the mirror charge is being charged. FIGS. 1 through 3 of the accompanying drawings illustrate the relationship between time and a load imposed on the motor in the above three charging methods, the horizontal axis being indicative of time t and the vertical axis being indicate of required motor force P. When the mirror and the shutter are simultaneously charged as indicated by the lines (a), (b), respectively, in FIG. 1, the load imposed on the single motor is increased. This mode requires an increased number of speed reducing gears in order to increase a speed reduction ratio for the motor power, and hence the power transmission efficiency is reduced. Use of two motors would speed up the film winding, but would result in an increased cost and be difficult to implement due to the limited space available in the camera. When the shutter is charged as indicated by the line (b) in FIG. 2 after the mirror has already been charged as shown by the line (a), the speed reduction ratio may be small, but the time it takes for the mirror and the shutter to be fully charged is longer. Attempts to shorten the charging time would reduce the mechanical strength, particularly durability, of the members to be charged.
The third method, in which initiation or charging of the shutter occurs while the mirror is being charged as shown in FIG. 3, is advantageous over the former two methods in that the load exerted on the motor when the latter starts being energized is low, and hence the shutter and the mirror can be charged smoothly; no additional gears are necessary for the purpose of increasing the speed reduction ratio, and the members to be charged have an improved degree of durability.